Power line protective system



Feb. 21, 1939. L. F. HUNT POWER LINE PROTECTIVE SYSTEM Filea Dec.

28, 1936 4 Sheets-Sheet l Feb. 21, 1939. F. HUNT POWER LINE PROTECTIVE SYSTEM Filed Dec. 28, 1936 4 Sheets-Sheet 2 12/97/02" 14 a w FGZA/T ifw Feb. 21, 1939.

L, F. HUNT POWER LINE PROTECTIVE SYSTEM Filed Dec. 28, 1936 4 SheetsSheet 4 rz ewfor 44 0/0 F Patented Feb. 21, 1939 UNITED STATES,

PATENT OFFICE 6 Claims.

This invention relates to electrical protective systems and relates more particularly to protective systems for electrical distribution or transmission systems. A general object of this invention is to provide a practical, dependable, and highly sensitive protective system of the character referred to.

Another object of this invention is to provide improvements in the general type of protective equipment described in United States Letters Patent No. 1,965,896, issued to L. F. Hunt and F. B. Doolittle, July 10, 1934.

The patent referred to above discloses a protective system for an electrical distribution system that is unaffected by or unresponsive to the rather rare or infrequent balanced fault conditions and instability resulting from the synchronous machines of the system falling out of step with each other, and that is designed to function and protect the distribution system against all other fault conditions. In practice-it has been found that a protective system of the character disclosed in said patent is not applicable to all installations and does not properly operate under certain conditions where the line current drops below the normal current range when a phase to phase fault occurs.

Another object of this invention is to provide a protective system of the character referred to that is sensitive to and that will operate under phase to phase fault conditions to select and clear from the distribution system sections of the line involved in such a fault, irrespective of the current carried thereby during such a fault.

Another object of this invention is to provide a protective system of the character mentioned that embodies balanced current detector relays and balanced current trip relays so related that the system will select and clear the affected line section or sections in the event of undercurrent conditions resulting from a phase to phase fault, as well as unbalanced overcurrent conditions resulting from similar faults.

Another object of this invention is to provide a protective system of the character mentioned in which the detector relays and the trip relays may be very rapid or instantaneous.

A further object of this invention is to provide a protective system of the character mentioned embodying control relays so related with the other elements of the system that they prevent premature operation of the trip relays whereby the trip relays may be very rapid or instantaneous relays.

The various objects and features of my invention will be fully understood from the following detailed description of typical preferred forms and applications of my invention, throughout which description reference is made to the accompanying drawings, in which: 5

Fig. 1 is a diagrammatic view of a typical power distributing system embodying the protective system of the invention. Fig. 2 is an enlarged diagrammatic view illustrating the details of one form of protective unit provided by the invention. Fig. 2 is an across the Wire diagram of the A. C. circuits shown in Fig. 2. Fig. 2 is an across the wire diagram of D. C. circuits shown in Fig. 2. Fig. 3 is a view similar to Fig. 2 illustrating another form of unit and Fig. 4 is a more or less diagrammatic view of a type of relay that may be employed to advantage in the system.

The protective system of the present invention is adapted for use in connection with power distributing systems in which the power is handled by means of any of the typical wiring systems used in such installations. In the following detailed description I will describe typical forms of the invention as applied to a well known type of wiring system. It is to be understood that the invention is not to be considered as limited or restricted to this particular application. Further, it is to be understood that the invention is primarily concerned with a protective sysem and is not directly concerned with the mechanical de- 3 tails of the various relays, transformers, or other equipment involved. Accordingly, the invention has been illustrated in a diagrammatic manner to be better understood by those skilled in the art.

Fig. 1 of the drawings illustrates diagrammatically a protective system of the invention as applied to a typical power distributing system while Figs. 2 and 3 illustrate different forms of units of the protective system which units embody features of the invention. The typical electrical distributing system illustrated in Fig. 1 includes two spaced sources of power A and B connected by main power conductors In, H and I2 of one circuit and main power conductors I U I l and I2 of a parallel circuit. The circuits extending between the power sources A and B are divided by sub-stations C, D and E into a plurality of line sections F, G, H and I.

The present invention provides a protective unit X of the character illustrated in Fig. 2 at each end of each line section F, G, H and I of each of the power circuits. The several units X are interconnected by a signal system to constitute the protective system of the invention. I 55 protective system.

will first describe in detail one of the units X and will then describe its operation and its relationship to the other units X as employed in the It is to be understood that the description of this unit X is equally applicable to the other units X of the system. Following the description of the unit X illustrated in Fig. 2, I will describe in detail the unit X illustrated in Fig. 3.

The particular protective unit X illustrated in Fig. 2 is connected with the main conductors H), H and I 2 of one of the main circuits being located at one of the substations C, D or E. This substation has bus bars l3, l4 and i5 connected with the main lines I0, II and i2, respectively.

The unit X includes a circuit breaker iii connected with the main power lines re, ii and I2 ahead of the points of connection of the buss bars I3, it and !5 with the lines. The circuit breaker i5 is adapted to be operated by current from an outside source carried by lines I? and E8. The energizing lines H and 18 of the circuit breaker l6 are controlled by trip relays I9, 26 and 25 and a trip relay 22. Closing or operation of any of the trip relays I9, 20, 2| or 22 completes the energizing circuit to the breaker l6, as will be hereinafter described.

In accordance with the invention the trip relays 19, 20 and 2f are balanced current relays. The trip relays l9, 2% and 2! include movable contacts W 20 and 2l respectively, for controlling the operating circuit of the breaker l6 in the manner to be hereinafter described. The

contacts I9 20 and Zi respectively, for conunder normal line conditions current from onephase of the line section flows through the closing or operating coils of a trip relay I9, 28 or 2!, tending to close its contact While current from another phase of the line section flows through the restraining coil of said relay to restrain or prevent closing of the contact.

The coils I9 20, 21 and W 25 and 2! are supplied with current by the lines to be hereinafter described, so that an unbalanced current condition between any two main power lines H], H or !2 in the line section with which the unit X is connected results in the closing or operating of one of the trip relays. i9, 28 or 2!. In practice the operating and restraining coils of the trip relays I9, 20 and ill may be related so that the relays operate under any selected differential in current. For example, the restraining coils 19, am and 2i may have 10% more windings than the operating coils l9, 20 and 2l so that there must be more than 10% more current flow through the operating coils than through the restraining coils to effect the operation of the trip relays. This relationship or setting may be varied to suit various installations, etc. If desired, the restraining coils l9 2t! and 2l may be assisted by springs tending to hold the contacts 59 28 and 2| against closing. In accordance with the invention the trip relays i9, 20, 2! and 22 are pref erably time delay relaysf The trip relay 22 includes a movable contact 22 controlled or operated by a closing coil 22. The contact 22;? may be normally held in the open position by a spring, by gravity, or by any other suitable means.

The trip relays I9, 20, 2| and 2 2 are connected or interposed in the operating circuit li-l8 of the circuit breaker 6 to control the same. In the particular arrangement illustrated the auxiliary power line H? is extended to the trip relays I9, 2H, 2! and 22 having two branches 53 and la between which the trip relays are connected or interposed. The trip relays E5, 2E, 23 and 22 have stationary contacts i9 29*, 2 l and 22 respectively, connected in the power line branch W The trip relays I9, 26, 2E and 22 have stationary contacts 2%, Zl and 22 respectively, connected in the branch W of the auxiliary power line 18. The trip relays 59, 2B, 2! and 22 are normally open, that is, their movable contacts 59 22 Zi and 22* are out of engagement with their stationary contacts so that the circuit to the circuit breaker id is normally open. It will be apparent that closing of any one of the trip relays I9, 2!], 2i or 22 completes the energizing circuit to the breaker it.

The means for controlling the trip relays 19, 2B and 2! described above, include a potential transformer 23, a current transformer 26, a directional relay 25 associated with the transformers 23 and 2d to be responsive to direction in current flow, detector relays 26, 21, and 23 and other relays and elements tobe hereinafter described.

The current transformer 24 may be applied to the main power lines If I l and i2 of the line section while the potential transformer 23 may be associated with the bus bars l 3, Id and 55, as illustrated. The potential transformer 23 has two primary windings 3B and 3! connected with the bus bars it, it and i5, and secondary windings 32 and 33 connected with the directional relay 25 by connections 3d, 35 and 35. The line or connection 35 is grounded. The current transformer 24 includes three windings 37 31 and 31 related respectively with the main power lines H3, l l and I2. The windings 31 31 and Si are connected with a common line 38 and lines 39, 30 and 41 extend from the windings 31*, 3'5 and 31, respectively, to the directional relay 25 about to be de scribed.

The directional relay -25 includes a rotatable element or unit &2 carrying spaced discs 43 and Q5 and carrying a contact 45. Contact G5 is adapted to engage a stationary contact 41 connected with the line 48. A fixed field element 49 is related to the disc 33 to dampen rotation of the unit 42. The operation or turning of the unit 42 is effected by windings 5t and 5! related to the disc 433 and windings 52, 53, 5'3 and 55 associated with the disc 44. The line 39 from the transformer winding 31 is connected with one pole of the winding 5'3. A line 55 extends from the other pole of the winding 55 to the relay 2?. The line 34 from the secondary windings of the potential transformer 23 connects with one pole of the winding 55 and a line 5? extends from the other pole of the winding 5| to one pole of each of the windings 53 and 55. The transformer line 36 is connected with the other pole of the winding 53 while the transformer line 35 is connected with the other pole of the winding 55. The transformer line H is connected with one pole of the winding 52 while a line 58 extends from the other pole of the winding 52 to the detector relay 28. The transformer line is connected with one pole of the winding 55 and a line 59 extends from the other pole of the winding 54 to the detector relay 26.

It is an important feature of the invention that the detector relays 26, 2'1 and 28 are balanced current relays. The detector relay 26 includes two stationary contacts 60 and 6| and a movable contact 62 for cooperating with the contacts 60 and 6|. The contact 60 is connected with the line 48 from the relay 25 while the contact 6| is connected with line 63. The movable contact 62 of the detector relay 26 is controlled by an operating winding 64 and a restraining winding 65.

The relay 21 includes two stationary contacts 66 and 61 and a movable contact 68 for cooperating with the contacts 66 and 61. The stationary contact 66 is connected with the line 48 from the directional relay 25. Stationary contact 61 is connected with the above mentioned line 63. The movable contact 68 of relay 21 is controlled by an operating winding 69 and a restraining winding 10. Detector relay 28 includes two stationary contacts 1| and 12 and a movable-contact 13 for cooperating with the contacts 1| and 12. Contact H is connected with the line 48 from the directional relay 25 and contact 12 is connected With the line 63. The movable contact 13 of the relay 28 is controlled by an operating winding 14 and a restraining Winding 15.

The above mentioned sets of operating and restraining coils or windings of. the directional relays 26, 21 and 28 may be set to effect the operation of the relays under any selected differential in current in the coils. In other words the operating and restraining windings of the detector relays 26, 21 and 28 may be related so that the operating coils are capable of overcoming the restraining coils when there is a given or selected differential in current in the coils.

The operating and restraining coils of the relays 26, 21 and 28 are associated with the directional relay 25 and with one another so that a detector relay 26, 21 and 28 operates when there is a differential of current of a given magnitude in any two of the main power lines I0, II and |2 of the line section, resulting from a phase to phase fault.

The operating coils I9, 20 and 2I and the restraining cells I 9, 2!! and 2 I of the trip relays I9, 20 and 2|, respectively, are interconnected with the operating and restraining coils of the trip relays 26, 21 and 28. I will now describe the interconnections between the several operating and restraining coils of the trip relays I9, 20 and 2| and the detector relays 26, 21 and 28. The line 59 extending from the directional relay 25 is connected to one pole of the operating coil 64 of the relay 26. An interconnecting line 16 connects the other pole of the winding 64 with the restraining coil of the detector relay 21. A line 11 extends from the other pole of the restraining coil 10 to one pole of the restraining coil I9 of the trip relay I 9.- A line 8| extends from the other pole of the coil I9 to one pole of the operating winding 20 of the trip relay 20. Line 59 is connected with the transformer winding 31 through the medium of the line 40 and the coil 54, as described above. Thus it is seen that the operating coil 64 of the detector relay 26, the restraining coil 10 of the detector relay 21, the restraining coil I9 of the trip relay I9, and the operating coil 20 of the trip relay 20 all carry current from the transformer winding 31 associated with the main power line H.

The line 56 extending from the directional relay 25 and connected with the transformer winding 31 is connected with'one pole of the operating coil 69 of the detector relay 21. An

interconnecting line 16 connects the other pole.

of the winding 69 with one pole of the restraining coil of the detector relay 28. A line 19 extends from the other pole of the coil 15 to one pole of the restraining coil 2| of the trip relay 2|. A line 80 extends from the other pole of the restraining coil 2| to one pole of the operating coil I 9 of the trip relay I9. With the connections just described the operating coil 69 of the detector relay 21, the restraining coil 15 of the detector relay 28, the restraining coil 2| of the trip relay 2| and the operating coil I9 of the trip relay I9 all carry current from the transformer winding 31 connected with the main power line I0.

The line 58 which extends from the directional relay 25 and which carries current from the transformer winding 31 is connected with one pole of the operating coil 14 of the directional relay 28. An interconnecting line 83 connects the other pole of the coil 14' with one pole of the restraining coil 65 of the detector relay 26. A line 84 extends from the other pole of the coil 65 to one pole of the restraining coil of the trip relay 20. A line 85 connects the other pole of the coil 20 with one pole of the operating coil 2| of the trip relay 2| Thus it is seen that the operating coil 14 of the detector relay 28, the restraining coil 65 of the detector relay 26, the restraining coil 20 of the trip relay 20, and the operating coil 2| of the trip relay 2| are all energized by current from the transformer winding 31 associated with the main power line I2.

The operating coils I9, 20 and 2l of the trip relays I9, 20 and 2|, respectively, each have a post connected with a common line 86 which in turn is connected with the ground or common line 38 of the transformer 24 through the connections to be hereinafter described.

The invention includes a transmitting relay 81 for controlling a transmitter T. The transmitting relay 81 includes a movable contact 88, a coil 89 for operating the contact 88 and four stationary contacts 90, 9|, 92 and 93 engageable by the contact 88. The operating coil 89 of the transmitting relay 81 is under the control of the directional relay and the detector relays 26, 21 and 28 to be energized upon the occurrence of unbalanced current flow in the line section in only one direction. A connection 94 connects one pole of the operating coil 89 with the auxiliary power line I1. A line 95 connects the other pole of the coil 89 with the movable contact 45 of the directional relay 25. Thus upon closing of the contact 45 against the contact 41 the operating coil 89 of the transmitting relay 81 is energized to shift the contact 88 against the contacts 90, 9|, 92 and 93. Lines 96 and 91 extend from the contacts 90 and 9| respectively, to the transmitter T. A line 98 connects the stationary contact 93 with the auxiliary power line I8 at a point ahead of the branch line I8.

The unit X includes a control or lock out means for locln'ng out the trip relays I9, 20, 2| and 22. In the form of the invention illustrated this means constitutes a lock out relay 99 for short circuiting the operating coils of the trip relays I9, 20, 2| and 22. The relay 99 includes a movable contact I00 and four stationary con tacts I01, I02, I93 and I04. -The stationary contact MI is connected in the line 85 supplying current to the coils 2l and 20 The stationary contact I02 is connected in line 8| supplying current to the coils 20 and I9. Contact I03 of relay 99 is'connecte'd in line "suppl'ying currentto the coils I9 and 2I with the common line 38 of the transformer 24 through the medium of the groundr'elay I to be subsequently described. The movable contact I99 of the lockout relay 99 is operated by acoil I96. A lead IIII connects one pole of thecoil Hit With the contact 92 of. the transmitter relay 8?. A lead I98 connects the other pole of the operating coil I96 with the auxiliary power line I]. Thus upon operation of the transmitter relay 81 'currentis supplied to the operating coil I96 of the lock out relay 99 from the lines I"! and I8 through lines I98, I97, contacts-"Maud 93 and line 98. It'will be seen that the lock out relay 99 is under the control of the transmitter relay 81 which in turn is governed by the directional relay 25 and the detector relays 26, 21 and 28.

The unit X further includes meansresp'onsive to phase to ground fault conditions for operating the circuit breaker IS. The ground fault re sponsive means includes a ground transformer I99, the ground directional relay I05, a relay H0 and the above described trip relay 22.

The groundbank'or ground transformer I99 may comprise three primary windings I 'II connected with the 'busb'ars I3, I4 "and I5. The primary windings IiI of the transformer I99 are connected to a common ground H2. The transformer I99 further includes's'econdary windings H3 connected in series ina line H4. A winding H5 is related to the line H4 to have current flow induced therein from the line II4.

The ground directional relay I95 is associated with the ground transformer 'I 99 tober'esponsive to ground current which may result from a ground fault and is associated with the current transformer 24 to detect the direction of such ground current flow. The ground directional relay I55 includes a turn'able element or unit 'I I6 carrying a disc III and a contact H8. The contact H8 is adapted to engagea'stationary contact II9. A line I29 extends from the stationary contact I I9 to the line 95 which in turn extends to the coil 89 of the transmitter relay 81. A fixed field element I2I is related to the disc III to dampen rotation of theunit 'I Hi. The ground relay I95 includes windings I22 and I23 related to the disc II? to effect turning of the unit H6. The common line 38 of the transformer 24 is connected with one pole of the winding I22 and a line I24 extends from the other pole of the winding I22 to the relay I Ill. The coil or winding I23 is connected in series with'the induction coil II5 bya line I25. A line I26 extendsfro'm the movable contact 'I I8 of the relay I05 to the relay H0.

The relay III) is a ground overcurrent relay comprising a movable contact I21 and two stationary contacts I28 and I29 engageable by the contact I'2II. The stationary contact I28 of the relay III] is connected with the above described line 63. The stationary contact I29 is connected with the line I26 extending from the contact N8 of the ground directional relay I955. The contact I 21 of the relay H9 is operated by a winding or coil I49. The line I24 extending from the coil I22 of the relay I95 is connected with one pole of the operating winding I49. A line I4I connects the other pole of the winding I49 with the stationary contact I94 of the lock out relay 99. The operating coil 22 of the trip relay 22 has one pole connected with the common line 86 and has its other pole connected with the line Contact I04 is connected Each unit X of the protective system includes a transmitter T and a receiver R. The transmitter T and the'receiver R. of a unit X may be provided in aset'as diagrammatically illustrated in the drawings. The transmitter and receiver set of the unit X has one pole connected to ground through'a suitable connection I39 and may have its other pole connected with one of the main power lines II), II or I2. In the caseillustrated a connection I9I connects said other pole of the receiver and transmitter set with the line I I. The line H is provided with 'a radio frequency trap I32. The connecting line I3I is provided with a coupling capacitor I93. While I'haveillustrated a radio type of interconnection between the'units X it is to be understood that othersuitable forms'of interconnections may be employed. The transmitter TM a unit X is associated with itstransmitting relay 81 as described above, by'the lines Miami 9?. A line I35 connects on'epole of the'receiver'R with the auxiliary powerline'Itl while a line I36 connects the other pole of the receiver R with a terminal of the operating 0011196 of'the lock out relay 99.

The operation'of the protective system of the invention embodying the units X of the charac ter described above, is as follows:

In the event there is a balanced three phase fault in any one of the 'line sections F, G, H, or I, or in the event there is a balanced current flow inthe protectivesystem due to instability in the main power circuit, the current in the operating coils and the restraining coils of the detector relays 26, 21 "and '28 and of the trip relays I9, 20 'and M will be balanced and the contacts of the said relays will remain open with the result that the protective system will not function.

in the event that there is a phase to phase short circuit in oneof the line sections, say the line section H the units X at the opposite ends of the said section H operate in the same man'- ner as follows: Referring to Fig. 2 it will be seen that current will flow from the bus bars I3, I4 and I5 through the transformer 24 and the circuit breaker I6, and then by the main power lines to the short circuit. The short circuit current flow through the transformer 24 induces an unbalanced secondary current in the windings 31 31 'and 31 which are connected with the operating and restraining coils of the relays 26, '21 and 28 and of the trip relays I9,

20 and2-I. The faultcurrent flow from the bus 6 bars 13, I4 and I5 to the short circuit is such that the direction of the secondary current in I the windings-31 31 and 31 passes through the current coils 50, '54 and 52 of the directional relay 25 to turn the unit 42 in a direction to hold the contacts 45 and 41 open. The current in passing through the coils of the detector relays 25, 21 and 28clo'sesthe contacts of these relays but "since the contacts 60, BI, 66, 61, II and 12 of said relays are inseries with the open contacts of relay 25, the closing of the relays 2'6, 21 and 28 does not result in any further action. As described above, the operating coils and restraining coils of the trip relays I9, 20 and 2I' are connected in series with the operating and restraining coils of the, detector relays 26, 21 and 28 so that the current passes through the coils of the trip relays as well as the coils of the detector relays. In the fault condition under consideration the current in the operating and restraining coils of at least one of the trip relays I9, 20 or 2I is unbalanced with the result that at least one of the trip relays closes its contact. Closing of the contact [9 20 or Zi of a trip relay results in energization of the trip coil of the circuit breaker I6 by current supplied from the circuit II-I8. Tripping or opening of the breaker I6 clears the faulted line section of the main power system. The action or operation just described takes place in the units X at the opposite ends of the line section H, thus clearing the faulted section from the system.

When a phase to phase short occurs in a line section external to the line section I-I under consideration the direction of current from the transformer 24 is reversed in the associated relays of the units X at the ends of the line section H. This reversal of current flow in a unit X results in the closing of the contacts 45 and 4'! of the relay 25. As described above, a phase to phase short circuit results in energization of at least one of the detector relays 26, 27 or 28 due to unbalanced current conditions. Closing of a relay 26, 21 or 28 results in the connection of the line 48 with the line 63, the line 48 being electrically connected with the line 95 by the closed or engaged contacts 45 and 47. The electrical connection of the line 48 with the line 63 following operation of one of the relays 26, 21 or 28, completes the energizing circuit to the relay 81 through the lines 95, 48, 63 and 94, described above. This energization of the transmitting relay 8'! electrically connects contacts 92 and 93 so that energizing current is supplied to the coil I06 of the lock out relay 99 through the lines 98, I01 and I08. Energization of the lock out relay 99 results in short circuiting the operating coils of the trip relays I9, 20, 2I and 22 preventing the operation of the trip relays. The above described energization of the transmitting relay 8? puts the transmitter T into operation so that it sends a signal over the line to the receiver R of the unit X at the other end of the line. The transmitting relay 8! remains energized so long as the fault condition persists so that the trip relays are prevented from oper ating.

It is to be particularly noted that the detector relays 26, 2'! and 28, are balanced as described above, so that they are receptive to or responsive to an unbalanced current condition of any selected or desired magnitude. Accordingly, the detector relays 26, 27, and 28, are capable of operating under any unbalanced current condition resulting from a fault-in a section of the power line external to the section H or the section protected by the given unit X. This is important as it assures the proper operation of the detec tor relays 26, 27 and 28 under conditions where the current in the affected line section is less than the expected or normal load as well as under overload conditions. In other words the balancing of the detector relays 26, 27, 28 with any selected setting, as described above, renders the protective system more sensitive and responsive to any unbalanced current condition in a line section external to the section protected by the unit X embodying the said relays.

It is to be understood that when a phase to phase fault occurs on a line of the power system the other end of said section, which signal ef- 'fects the locking out of the last mentioned unit X so that its breaker I6 does not function. A unit X receiving a signal as just described is locked out as follows: The receiver R receiving the signal completes a circuit from the auxiliary power line I8 through the line I35, and the line I36 to the coil I06 of lock out relay 99 and thence through the line I08 to the line H. Thus the signal received serves to energize the lock out relay 99 to short circuit out the operating coils of the trip relays I9, 20, 2| and 22 so that the unit X is locked out.

In the event of a phase to ground fault on a line section protected by the units X the operation of the units is as follows: The current flow resulting from a phase to ground fault will be of sufficient magnitude to operate the relay H or the trip relay 22. The current supplied to the coil I 22 of relay I by the current transformer 24 flows through line I24, coil I40, line MI and line I43 to the coil 22 to operate the trip relay 22 and to operate the relay H0. Operation of the trip relay 22 of course results in opening of the circuit breaker I6. relay H0 is in this case only incidental owing to the fact that the contacts H8 and H9 of the ground relay I05 are open.

In the event of a phase to ground fault on a line section external to the section protected by the unit X under consideration the current flow in the winding I 22 is reversed resulting in turning of the unit H6 and closing of the contact H8 and H9. The operation of the unit X under these conditions is substantially the same as that just described except that closing of the contact H8 and H9 completes a circuit to the operating coil 89 of relay 8'! through connections 94, 95, I20, I26 and 63. The relay H0 is operated by an external ground fault as well as an internal ground fault, as mentioned above. Operation of the transmitter relay 8! results in closing or operation of the lock out relay 99 which prevents closing of the relay 22 so that an external ground fault does not effect tripping of the circuit breaker l8. Closing or operation of the transmitter relay 8'! due to an external ground fault does, however, result in operation of the transmitter T. The transmitter T sends a signal to the unit X at the other end of the line, as described above, to operate its lock out relay 99 to prevent operation of the trip relays by the external ground fault condition.

Fig, 3 of the drawings illustrates a form of protective unit X embodying a control relay I50. The relay i50 operates to prevent operation of the trip relays I8, 20, 2i and 22, pending the completion of the operation of the directional relay 25, the ground relay I05 and the detector relays 26, 27, 28 and H0. The protective unit X illustrated in Fig. 3 may be identical with the unit X described above, except that it embodies the relay I50 and lines and contacts associated with the relay I50 to effect its operation. Accordingly, corresponding reference numerals indicate corresponding elements in the protective units illustrated in Figs. 2 and 3. It is to be The operation of the understood that units X of the character illustrated in Fig. 3 of the drawings may be employed in the protective system in the same manner as the above described unit X.

The relay I50 includes two stationary contacts I5I and I52 and a movable contact I53 for cooperating with the stationary contacts. The movable contact I53 is normally in'coopera'tion with the stationary contacts I5I and I52 and is controlled by a winding or coil I54. A line I55 connects the stationary contact I5I with the stationary contact 92 of the transmitter relay 81. A line I56 connects the" other stationary contact I52 with the line 98 connected with the auxiliary power line I8. Thus when the movable contact I53 is in its normal position in cooperation with the contact I5I and I52 current is supplied to the coil I06 of the lock out relay 99 from the circuit I1 and I8 through lines 98 and I56, contacts I52, I53 and I5'I and. lines I55, I01 and I08. Accordingly, the lock out relay 99 is normally operated or energized to short circuit or look out thetrip relays I9, 20, 2I and 22,

The control relay I50 is associated with or controlled by thedetector relays 26, 21, 28 and H0 to be operated following operation of any one of the detector relays; One pole of the operating winding I54 of the relay I50 is connected with the auxiliary power line l1 by a line I51. A line I58 extends from the other pole of the winding I54 to the detector relays 26, 21,- 28 and H0. The detector relay 26 has a stationary contact I59 connectedto the line I58. The relay 21 has a stationary contact I60 connected to the line I58. Detector relay 20 has'a stationary contact I6I connected to the line I58 and detector relay IIO has a stationary contact I62 connected to the line I58. The contacts I59, I60, IOI and I62 are engageable by the movable contacts of the detector relays 26, 21, 28 and H0,

respectively, to complete a circuit from power lines I1 and I0 through the lines-63, I58 and I51 to energize the winding I54 of the relay I50. Operation of any one-of the detector relays 26, 21, 28 or IIO-is accompanied by or followedby operation of the control relay I50 which in turn breaks the circuit to the coil I06 of the lock out relay 99 to allow the trip relays I9, 20, 2I and 22 to function.

The operation of the unit X is substantially the same as the operation of the unit X described above, except that the lock out relay- 99 is normally energized and remains energized to prevent operation of the trip relays I9, 20, 2I and 22 until at least one of the detector relays 26, 21, 28 or H0 has completed its operation, whereupon the control relay I50 is energized to effect de-energization of the relay 99 and to allow the trip relays to function provided the line fault occurs in the line section protected by the unit X. Thus when a phase to phase short occurs in the line section protected by the unit X the relay 25 and certain of the relays 26, 21 and 28 are energized by current from the transformer 24 as described above. At this time the lock out relay99 is energized to prevent operation ofthe trip relays I9, 20 and 2|. Immediately upon energization of a detector relay 26, 21 or 28 by phase to phase fault current the energizing circuit is'completed to the coil I54 of the control relay I50 through the connections described above to operate the relay I50. Operation of the relay I50 elfects the de-energizationof the lock out relay 99 and immediately upon de-energization of the lock out relay 99 the'trip relays I9, 20 and 2I are conditioned for operation by the phase to phase fault current in the protective unit. Thus the trip relays I9, 20 and 2| are prevented from operating until the relay 25 and a detector relay 26, 21 or 28 have completed their operations. For this reason the trip relays I9, 20 and 2I may be very rapid or instantaneous relays.

In the event of a phase to ground fault in the line section protected by the unit X the opera"- tion is the same as just described, except that the ground relay I05 and the detector relay IIO function and following operation of the relay N0 the control relay I50 is operated to break the circuit to the coil I06 of the lock out relay 99". Immediately upon de-energization of the lock out relay 99 the trip relay 22 may function. This functioning of the relay 22 is subsequent to the complete operation of the relays I05 and H0 and, therefore, the relay 22 may be a very rapid or instantaneous relay.

Under fault conditions external to the line section protected by the unit X the unit X operates in the same manner as the unit X described'above, the balanced trip relays 26, 21, 28 and H0 being responsive to unbalanced line conditions irrespective of the magnitude of the current. This is important as it assures the proper functioning of the protective unit under all fault conditions except balanced three phase faults and instability. resulting from an out of step condition of the synchronous machines inthe power circuit. When an unbalanced fault occurs in aline section external to the line section protected by the unit X the detector relays 26, 21, 28 and I I0 effect the operation of the transmitter relay 81. The relay 81 operates to energize the transrfiitter T to send a signal along the line to the unitX at the other end of the line section and also operates to maintain the lock out relay 99 energized to preventoperation of the trip relays I9, 20, 2I and 22.

Fig. 4 of the drawings illustrates a type of balanced relay. that may be employed'in either of the above described protective units X or X of the invention where balanced relays are required. In other words the balanced detector relays 26, 21 and 28 of the units X and X and the balanced trip relays I9, 20 and 2| of X only may be of the type illustrated in Fig. 4. It is to be understood that the structure illustrated in Fig. 4 of the drawings is merely typical of the equipment that may be employed in the system of the invention, and this disclosure is not to be taken as limiting or restricting the invention to the use of this particular form of relay.

The relay illustrated in Fig. 4 includes a suitable base I10 carrying two spaced magnets I1! and I12. A post I13 projects from the base I10 between the spaced adjoining arms of the magnets I1! 'and I12. A winding or coil I14 which may be considered the restraining coil is provided on the outer pole I15 of the magnet HI and a winding or coil I16 which may be considered the operating winding is provided on the outer pole I11 of the magnet I12. Armatures or clappers I18 and I 19 are carried by a lever I to be attracted or operated by the coils I14 and I16. The clappers I18 and I19 are suitably insulated from the lever I80. The lever I80 is pivotally supported on the post I13 at NH. The lever I80 may carry a screw I82 projecting toward the arm I15 of the magnet I1l to adjust the air gapbetween the clapper'l18 and the magnet arm I15. The lever I80 may carry one or more insulated contacts I83 for cooperating with one or more stationary contacts I64 carried on a post I85. The coils I14 and I16 are related to normally maintain the lever I80 in a position where the contacts I83 and I84 are out of engagement. When the current in the coils I14 and I16 becomes unbalanced to a selected or predetermined degree, with the current in the operating coil greater than that in the restraining coil, the operatingcoil I16 overcomes the restraining coil I14 and draws the clapper I19 to the post I11 to bring the contacts I83 in engagement with the contacts I84. It will be readily understood that the coils I14 and I16 may be related to cause the operation of the relay under any desired or selected degree of differential in current supplied to or carried by the coils.

Having described only typical preferred forms and applications of my invention, I do not wish to be limited or restricted to the specific details herein set forth, but wish to reserve to myself any variations or modifications that may appear to those skilled in the art or fall Within the scope of the following claims.

Having described my invention, I claim:

1. A protective system for a sectional multiphase current carrying line including, a protective unit at each end of each line section, each unit including, current transformers for the several phases of a line section, potential transformers for the several phases of said line section, a circuit breaker, trip relays controlling the breaker and each including an operating coil and a restraining coil, a transmitting relay, balanced current detector relays, each including an operating coil and a restraining coil, each current transformer being connected with the operating coil of its related detector relay, coil of each one of the detector relays being connected in series with the restraining coil of another detector relay, with the restraining coil of one of the trip relays and with the operating coil of another trip relay, a directional relay energized by the current transformers and the potential transformers, the balanced detector relays and the directional relay jointly controlling the transmitting relay whereby the transmitting relay is only operated upon the occurrence of an unbalanced fault external to the line section with which the unit is connected, a lockout means for the trip relays, and a receiver controlling the look-out means and receptive to the action of the transmitting relay at the other end of the said line section.

2. A protective system for a sectional multiphase current carrying line including, a protective unit at each end of each line section, each unit including, a circuit breaker, current balanced trip relays controlling the breaker and each including a current operating coil and a current restraining coil, a transmitting relay, current balanced detector relays controlling the transmitting relay, and each including a current balanced operating coil and a current balanced restraining coil, a potential transformer for each phase of a line section, a current transformer for each phase of said line section, each current transformer being connected with the operating coil of its related detector relay, the operating coil of each one of the detector relays being connected in series with the restraining coil of another detector relay, with the restraining coil of one of the trip relays and with the operating coil of another trip relay, lock-out means for the trip the operating relays, a directional relay connected in series with the detector relays and the transmitting relay whereby the transmitting relay is under the joint control of the directional relay and the detector relays whereby it is only operated upon the occurrence of an unbalanced line flow in one direction out of the line section, and a receiver controlling the lock-out means and governed by the transmitting relay of the unit at the end of the said line section.

3. A protective system for a sectional multiphase current carrying line including, a protective unit at each end of each line section, each unit including, a circuit breaker, current balanced trip relays controlling the breaker and each including an operating coil and a restraining coil, current balanced detector relays each including an operating coil and a restraining coil, a potential transformer for each phase of a line section, current transformers for the several phases of said line section, each current transformer being connected with the operating coil of its related detector relay, the operating coil of each one of the detector relays being in series with the restraining coil of another detector relay, with the restraining coil of one of the trip relays and with the operating coil of another trip relay whereby a trip relay and a detector relay are operated upon an unbalanced current flow on the line section, a lock-out means for the trip relays, a transmitting relay controlling said lock-out means, an energizing circuit for the transmitting relay controlled by the detector relays, and a directional relay energized by the potential transformers and the current transformers and acting jointly with said detector relays to control said circuit whereby the transmitting relay is operated upon the occurrence of unbalanced line current flow in one direction only out of the line section.

4. A protective system for a sectional multiphase current carrying line including, a protective unit at each end of each line section, each unit including, a circuit breaker, current balanced trip relays controlling the breaker and each including an operating coil and a restraining coil, current balanced detector relays each including an operating coil and a restraining coil, a potential transformer for each phase of a line section, current transformers for the phases of a line section, each current transformer being connected with the operating coil of its related detector relay, the operating coil of each one of the detector relays being in series with the restraining coil of another detector relay, with the restraining coil of one of the trip relays and with the operating coil of another trip relay whereby a trip relay and a detector relay are operated upon an unbalanced current flow on the line section, lock-out means for the trip relays operable by the detector relays, and a directional relay energized by the potential transformers and current transformers and acting jointly with the detector relays to control the operation of the lock-out means whereby the trip relays are not freed for operation upon the occurrence of an unbalanced current in a single direction out of the line section.

5. A protective system for a sectional multiphase current carrying line including, a protective unit at each end of each line section, each unit including, a circuit breaker, current balanced trip relays controlling the breaker and each including an operating coil and a restraining coil, current balanced detector relays each including 7 control relay controlling the anoperating coilanda restraining coil, potential transformers for the phases of a line section, current transformers for the several phases of said line section, each-current transformer being connected with the operating coil of the related detector relay, the operating coil of each one of the detector relays being connected in series with the restraining coil of another detector relay, with the restraining coil of one of the trip relays and with the operating coil of another trip relay, whereby a trip relay and a detector relay are operated upon an unbalanced current flow on the line, a lock-out relay for the trip relays, a lock-out relay and energized by the detector relays, and a directional relay energized by said current transformers and said potential transformers and acting jointly with the detector relays to govern energization of the control relay whereby the trip relays are operable upon the occurrence of unbalanced fault condition external of a given line section.

6. A protective system for a sectional multiphase current carrying line including, a protective unit at each end of each line section, each unit including, a circuit breaker, current balanced trip relays controlling the breaker and each including an operating coil and a restraining coil, current balanced detector relays each including an operating'coil and a restraining coil, a current transformer for each phase of a line section, a potential transformer for each phase of said line section, each current transformer being connected with the operating coil of the related detector relay, the operating coil of each one of the detector relays being connected in series with the restraining coil of another detector relay, with the restraining coil of one of the trip relays and with the operating coil of another trip relay, whereby a trip relay and a detector relay are operated upon an unbalanced current flow on the line section, a transmitter, a lock-out relay for the trip relays, a transmitter relay controlled jointly by the detector relays and the directional relay for energizing the transmitter and operable to actuate the lock-out relay, a normally de-energized control relay normally energizing the coil of the look-out relay and energized by any one of the detector relays, and a directional relay energized by the potential transformers and current transformers and acting jointly with the detector relays to control the operation of the look-out relay whereby the trip relays are freed for operation upon'the occurrence of an unbalanced current line flow in a single direction out of said-line section.

LLOYD F. HUNT. 

